There is also sleep deprivation, lucid dreaming, holotropic breathing. The latter is often practiced in big cities and it is very easy to find the desired section in Google. There, about twenty people sit on mats and breathe to the music, driving themselves into a trance. Everything is safe and under the supervision of experienced people. Another interesting thing is sleep deprivation, which, on the twentieth day, can cause an effect comparable to a powerful dissociative drug (the causal link is partially turned off, the world is falling apart before our eyes, revealing its secret nooks). It does not imply a complete rejection of sleep, but a limitation of up to one to three hours a day, depending on the stage. Because in a couple of weeks you will need to force yourself to sleep. True, the recovery period after such an experiment takes a long time and is accompanied by depression. But still, this is a very powerful experience after which life will not be the same.
Even six years ago I organized a group of people in a jabber conference, which jointly tried to overcome the desire to sleep. Of the twenty people, only three were able to make it to the end. At the end, each had a list of template phrases for communicating with others, because it was not possible to give a quick answer, the reactions were very slow, which aroused suspicion.
There are many visual illusions, looking at which at a certain time, the picture of perception will change slightly, and for a short time you can observe how everything "floats" or "fuses". There are also certain sounds that can give rise to acoustic hallucinations, such as "white noise", when listening to which you can hear voices or something similar. To do this, you need to tune the radio between radio stations and listen for about 2 minutes. It doesn't always work, but it often works, although it depends on the person. Also, the psyche is affected by frequencies below 20 Hz, but caution is needed here, since infrasound can harm the body and psyche.